The present invention relates generally to acoustic emission monitoring and more particularly to a method and system to detect unwanted noise.
There are many instances when it is desirable to analyze an acoustic signal. This is especially true in the automotive field when determining how much noise will be heard by the occupants of a motor vehicle. Depending on the level and type of noise, it is often a desire to reduce any noise to provide a motor vehicle with quiet operating characteristics.
Eliminating noise can best be accomplished by eliminating the source of the noise. Because noise, especially in motor vehicles, is a composite of many different noises, the source is often difficult to identify. Most of the noise in motor vehicles is generated by the powertrain, the interaction between the road and the tire, and the wind created under driving conditions. These three types of noise have different characteristics and generally generate random noise. For example, the overall noise at a specific speed may have a substantially different characteristic if the powertrain is providing substantial torque at that speed. Likewise, the overall noise may be affected by the condition of the road on which the motor vehicle is traveling. Therefore, there is a need to isolate the sources of overall noise under various operating conditions.
Specifically, industry has been trying to objectively measure the squeak of stabilizer bar bushings for years without success. Industry has not succeeded mainly because of acoustic contamination by background noise, i.e., surrounding equipment, fan, etc. Also, the frequency band being examined was typically lower than 2000 Hz. In lieu of an objective measurement, industry has resorted to relying on subjective evaluations that depend significantly on operator perception.
It would therefore be desirable to have a way to objectively measure stabilizer bar bushing squeak while eliminating the need for subjective evaluations. Additionally, it would be desirable to make the determination of bushing squeak more consistent and reliable.
It is an object of the invention to provide an improved and reliable method and system to detect unwanted noise. Another object of the invention is to provide a way to objectively measure unwanted noise while eliminating the need for subjective evaluations. An additional object of the invention is to make the determination of unwanted noise more consistent and reliable.
Accordingly, an apparatus for detecting unwanted noise over background noise, which is generated by a noisy source, is disclosed. In one aspect of the invention, an apparatus for detecting unwanted noise includes a reference sensor that generates a reference signal in response to stimulation by a source. A combined noise detector picks up a combined noise signal, which includes both background noise and the unwanted noise generated by the source. A noise separation synthesis device filters both signals to generate a coherent unwanted noise signal from the combined noise signal as a function of the reference signal generated by the reference sensor. A comparator determines the presence of unwanted noise by calculating the Kurtosis value of the coherent unwanted noise signal.
The present invention achieves an improved and reliable method and system to detect unwanted noise. One advantage associated with the present invention is the ability to analyze components of a signal by filtering then out of the signal in the time domain rather than in the frequency domain.